Ictal and Interictal. Surface of EEG patterns in epilepsy

Extracranial electroencephalogram [EEG] is an important neurodiagnostic test in the diagnosis and evaluation of epileptic disorders. Interictal extracranial EEG patterns are categorized into non specific patterns such as distorted normal EEG patterns or abnormal slow activity which indicate neurophysiological disturbance or cortical dysfunction related to seizures, epileptic lesions or antiepileptic drugs. Non specific EEG patterns are focal or generalized. Specific interictal EEG patterns are patterns of interictal epileptic discharges [IEDs] and include spikes, sharp waves or spike slow wave complexes. Interictal epileptic discharges are focal or generalized. Detection of IEDs on extracranial EEG depends on the seizure type, epileptic syndrome, location of the epileptic focus in partial epilepsies, age of seizure onset and methodology of recordings. Ictal EEG patterns provide valuable clues for diagnosis of epileptic and non-epileptic episodes, classification of epileptic syndromes and localization of epileptic foci in intractable partial epilepsies for epilepsy surgery. This syllabus provides an introduction to common interictal and ictal patterns in extracranial EEG and discusses limitations of extracranial EEG recordings